The fan assembly of a turbofan gas turbine engine comprises a fan rotor having a plurality of generally axially extending slots in its periphery, which receive the root portions of the fan blades. The slots and fan blade root portions are of corresponding generally dovetail cross-section shape so as to ensure radial retention of the fan blades.
Our European patents EP0597586B1 and EP0690203B1 disclose a fan blade assembly of a turbofan gas turbine engine in which the fan blade root portions and the axially extending slots are provided with generally radially extending slots. The radially extending slots in each fan blade root portion are aligned with the radially extending slots in the corresponding axially extending slot in the periphery of the fan rotor. A U-shaped key is located in each of the sets of aligned radially extending slots to lock the fan blade root portions in position. Each key is provided with a spring to bias the key into the aligned radially extending slots and each key is moved against the spring and out of the radially aligned slots to allow the fan blade root portion to be moved axially for assembly or disassembly of the fan blades on the fan rotor. Locking means are provided in the axially extending slots between the fan blade root portions and the bottoms of the axially extending slots to lock the keys in position in the aligned radially extending slots. Additionally rubber pads are provided between the locking means and the bottoms of the axially extending slots to provide a tight, vibration free fit for the locking means and to prevent movement of the fan blades in the axial and tangential directions of the fan blade assembly during windmilling of the fan blade assembly.
In a variation of this arrangement springs are provided between the locking means and the bottoms of the fan blade root portions to provide a tight, vibration free fit for the locking means and to prevent movement of the fan blades during windmilling of the fan blade assembly.
The fan blade root portions and the springs between the locking means and the fan blade root portions are provided with wear resistant coatings to reduce wear or fretting.
These arrangements have proved satisfactory for turbofan gas turbine engines for fan blade assemblies with current sizes of fan blades.
There is a requirement for turbofan gas turbine engines with fan blade assemblies with larger, longer, and heavier fan blades.
However, the use of the existing arrangements is unsatisfactory because the forces required to prevent movement of the fan blades during windmilling of the fan blade assembly are too high to allow assembly and disassembly of the fan blades into the fan blade assembly and/or if the fan blades are assembled into the fan blade assembly the wear resistant coatings on the springs and fan blade root portions are rubbed off.